7. EF Core 多导航属性配置

一、多导航属性配型

在 Post 类中，可能需要跟踪是文章的创建者和最后编辑者，下面是 Post 类的两个新的导航属性。

1、设置导航属性方式

public class Post
{
 　　public int PostId { get; set; }
 　　public string Title { get; set; }
 　　public string Content { get; set; }
 　　public User Author { get; set; }
 　　public User Contributor { get; set; }
}

public class User
{
 　　public string UserId { get; set; }
 　　public string FirstName { get; set; }
 　　public string LastName { get; set; }

 　　[InverseProperty(nameof(Post.Author))] //设置反转导航属性
 　  public List<Post> AuthoredPosts { get; set; }
 　  [InverseProperty(nameof(Post.Contributor))] //设置反转导航属性
     public List<Post> ContributedToPosts { get; set; } 
}

在Post类设置反转导航属性也可以

public class Post
{
 　　public int PostId { get; set; }
 　　public string Title { get; set; }
 　　public string Content { get; set; }

    [InverseProperty(nameof(User.AuthoredPosts))]
 　　public User Author { get; set; }
    [InverseProperty(nameof(User.ContributedToPosts))]
 　　public User Contributor { get; set; }
}

public class User
{
 　　public string UserId { get; set; }
 　　public string FirstName { get; set; }
 　　public string LastName { get; set; }
 　 public List<Post> AuthoredPosts { get; set; }
    public List<Post> ContributedToPosts { get; set; } 
}

 Post表会默认生成:“导航属性名Id” 的外键  AuthorId,ContributorId

2.ForeignKeyAttribute方式设置

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    public User Author { get; set; }
    public User Contributor { get; set; }
}

public class User
{
    public string UserId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public User Author { get; set; }
    [ForeignKey("AuthorID")]
    public string ContributorID { get; set; }
    [ForeignKey("ContributorID")]
    public User Contributor { get; set; }
}

3.Fluent API方式

modelBuilder.Entity<Post>().HasOne(p => p.Author).WithMany(u=>u.AuthoredPosts).HasForeignKey("AuthorId");
modelBuilder.Entity<Post>().HasOne(p => p.Contributor).WithMany(u => u.ContributedToPosts);

二、Fluent API显示设置外键

referenceCollectionBuilder.HasForeignKey(p => p.BlogForeignKey);
modelBuilder.Entity<Car>().HasKey(c => new { c.State, c.LicensePlate });
referenceCollectionBuilder.HasFoHasForeignKey(s => new { s.CarState, s.CarLicensePlate }) //设置有复合主键表的外键，依赖主体要定义CarState,CarLicensePlate 这两个复合主键的属性字段
referenceCollectionBuilder.HasForeignKey("BlogId");